The present invention relates generally to reducing electro-magnetic interference between a mobile station and a hearing aid.
Hearing aids typically include electronic circuits for amplifying audible sounds, such as those provided by a speaker, a voice, an instrument, etc., so that a hearing impaired individual can better hear. A hearing aid may also include processing circuits for processing the audible sounds to improve the quality of the sound heard by the individual by, for example, filtering noise from the audible sounds received by the hearing aid. However, in noisy environments, such as a shopping mall, a city street, concert halls, etc., the hearing aid may have difficulty removing the noise without also removing the desired audible sounds.
To address this problem, some hearing aids may include electro-magnetic processing circuits in addition to the audio amplification and processing circuits. The electro-magnetic processing circuits sense and process electro-magnetic signals received by an electro-magnetic receiver in the hearing aid, such as a T-coil, to create sound waves that enable the hearing impaired individual to hear sound corresponding to the received electro-magnetic signals. This feature is particularly useful in any environment where desired audio signals are used to generate electro-magnetic signals. For example, an individual may switch the audio amplification circuits off and switch the electro-magnetic processing circuits on while talking on a cellular telephone. In so doing, the individual hears audible sound generated by the hearing aid in response to electro-magnetic signals produced by the cellular telephone speaker while effectively blocking out the “audible” environmental sounds.
Unfortunately, electro-magnetic processing circuits also detect other electro-magnetic signals, such as the electro-magnetic signals produced by various electronic circuits associated with the cellular telephone. As a result, sound generated by the electro-magnetic processing circuits in the hearing aid may be distorted. Further, while the electro-magnetic signals generated by the cellular telephone circuits do not generally interfere with the operation of the cellular telephone, they may interfere with the operation of a nearby electronic circuit external to the cellular telephone, i.e., the audio amplification circuits and/or the electro-magnetic processing circuits of a hearing aid. Therefore, electro-magnetic interference (EMI) generated by a cellular telephone typically degrades the performance of a hearing aid.